MATERIALS 21 



Hypogene forces, which produce metasomatism in 

 rock-masses buried to a great depth or involved in crustal 

 movements, may cause distortion, recrystallization, or 

 even magmatization of materials affected. An essential 

 feature of such action is the re-grouping of molecules^ 

 either into new crystals of the original minerals, or 

 into entirely fresh mineral types. A quartzite may 

 occasionally retain rough indications of the fossils that 

 were once embedded in it ; the refractory nature of 

 quartz tends to reduce its reaction to metamorphic 

 forces. But a clay-slate, in which the annealed 

 micaceous flakes have slewed round to positions different 

 from those due to sedimentation, will involve its con- 

 tained fossils in the distortion and cleavage to which it 

 has been subjected. Phyllites and schists have under- 

 gone such complete recrystallization that neither the 

 original rock nor its contents are clearly recognizable. 

 Similarly, a marble results from complete rearrangement 

 of the calcite molecules of a limestone ; the saccharoidal 

 complex of crystals retains no biological indication of 

 organic origin. Finally, when heat and pressure are 

 applied in full force, rock-matter undergoes that mag- 

 matic " fusion " or intersolution that results later in 

 formation of " Igneous rocks." In these no suspicion 

 of organic structure or influence, possibly excepting 

 diamonds, can be expected to occur. The longer a 

 rock has existed, the greater has been its danger from 

 hypogene forces. Hence the record of the faunas of 

 ancient periods of the Earth's history tends to become 

 more imperfect as it becomes more remote.. Extra- 

 ordinary exceptions, such as those afforded by the wonder- 

 ful Cambrian fossils of British Columbia, or the almost 

 " Tertiary " quality of the Ordovician clays of Northern 

 Russia, serve merely to emphasize the tragic deductions 

 latent in this generalization. 



